A vang is an adjustable device fitted to the underside of a boom to control the raising or lowering of the boom.
Vangs typology can be divided into two basic types: soft vangs and mechanical vangs. The most widely used vangs, in particular for smaller boat are soft vangs. A typical soft vang includes a multiple purchase block and tackle system including two or more blocks or pulleys attached to the boom, and a single line having one end secured to one of the pulley systems, with the line having a free end which is pulled out and released manually by the sailor. A soft vang increases sail efficiency by pulling down on the boom in medium or heavy air, thereby increasing the tension in the leech and reducing the spill of wind.
Soft vangs can only be used to pull down the boom. Thus, in slight winds or when docked, a wire or rope topping lift must be used to support the boom. Use of a topping lift is extremely undesirable because it increases the wind drag of the sailboat. Mechanical vangs represent an improvement over soft vangs in that they may both pull down on the boom and hold up the boom, thus eliminating the need for a wire or rope topping lift. There are four basic varieties of mechanical vangs.
The first variety is a tackle-equipped rigid vang. These vangs generally comprise a set of telescoping spring-loaded aluminum tubes with a tackle rigging longitudinally associated therewith. When the tackle rigging is tightened, it applies a downward force on the boom and compresses the spring within the telescoping aluminum tubes. As the rigging is loosened, the spring within the telescoping aluminum tubes extends, thus providing support for the boom. Typically, the spring comprises a steel coil; however, compressed-gas cylinder springs are also used.
A second variety of mechanical vangs are screwdriven or “rotary” vangs. In a screw-driven vang, a large turnbuckle is lengthened or shortened by turning a wheel or a pair of handles in the middle of the turnbuckle. Although capable of providing both tension in the leech and supporting the boom, screw-driven vangs have the serious disadvantage of being difficult and slow to adjust because of their heavy nature.
A third variety of mechanical vang are hydraulic vangs. Hydraulic vangs typically consist of a cylinder filled with hydraulic oil and a piston. A hydraulic pump controlled from the cockpit actuates the piston inward or outward to control the height of the boom.
The fourth variety of mechanical vang are flexible column actuated vangs. This type of vang is actuaded with a device that is capable of being moved between a contracted position and an extended position. When the adjustment mechanism is moved to a contracted position, the column is forced to bow arcuately to an arched position and the boom is forced in a downward direction. When the adjustment mechanism is released to extended position, the arcuately bowed column straightens and exerts forces pushing the boom upwardly.
Mechanical vangs have several serious problems. For the first three types, the telescoping tubes must be carefully maintained to avoid corrosion. In addition, if water is allowed to leak into the telescoping tubes, the metal springs may be particularly subject to corrosion. The telescoping springloaded tubes of these vangs must also be carefully machined, making them relatively expensive. Finally, these vangs are susceptible to denting and bending from transverse forces. Such damage inhibits the telescoping of the tubes, degrading the vang's performance. The fourth type of mechanical vang does not give a lower limit to the boom movement, making some mainsail operation difficult. Moreover first and fourth mechanical vang type have the serious limitation that the boom hold up control come from a constant elastic force that always needs pull down tackle rigging in force to maintain the boom at the desired level even in slight wind or when docked.
For these reasons there is an unresolved need in the art of boom vang system to have a simpler and lighter mechanism with hight boom control performance.